Corrosion inhibitor composition containing zinc, sulfamate, and phosphate ions

ABSTRACT

A liquid corrosion inhibitor and method designed for use by water treatment plants for the control of corrosion of municipal, industrial, commercial and domestic metal piping systems, wherein, as the inhibitor is economically added to the flowing water supply in minute dosages, it passivates the surface of the metal piping as it deposits a self-controlled film of insoluble zinc phosphate. One of the preferred inhibitors is &#39;&#39;&#39;&#39;zincsulfamate-orthophosphate.&#39;&#39;&#39;&#39; To be effective, the pH must be controlled to within the range of 5-9.

1 United States Patent Murray [4 June 13, 1972 [s41 CORROSION INHIBITOR [56] References Cited COMPOSITION CONTAINING ZINC,

UNITED STATES ATENT SULFAMATE, AND PHOSPHATE IONS P S 2,155,046 4/1939 Griffith et a1. ..252/387 Invenwfl WIlham Bruce Murray, 929 Terraine 3,170,883 2/1965 Owen et al..... ....252/187 Av n L ng Be c lif- 90804 3,211,659 10/1965 Pikaar..... ....252/142 3,215,637 11/1965 Clerbois ....252/387 2 [22] 1970 3,580,934 5/1971 Murray et a1. ..252/389 [21] Appl. No; 83,203

Primary ExaminerRichard D. Lovering Related US. Application Data Assistant Examiner-Irwin Gluck 'b [60] Division of Ser. No. 76,221, Sept. 8, 1970, aban- Attorney J G1 Son Semmes doned, Continuation-impart of Ser. No. 892,842, May [57] ABSTRACT 5, 1969, abandoned.

A liquid corrosion inhibitor and method designed for use by 52 us. c1 ..252/387,21/2.7, 106/14, "s Plants for P 0f 9 n1c1pa1, industrial, commercial and domesnc metal piping 252/389, 252/391 systems, whereln, as the 1nh1b1tor is economically added to the [51] Int. Cl ..C23f 11/16, C251 1 1/18' flowing water pp y in minute dosages, it passivates the SUP Fleld Of Search face of the metal as i deposits a selflcontroned of 106/14 insoluble zinc phosphate. One of the preferred inhibitors is zinc-sulfamate-orthophosphate. To be effective, the pH must be controlled to within the range of 5-9.

9 Claims, No Drawings CORROSION INHIBITOR COMPOSITION CONTAINING ZINC, SULFAMATE, AND PHOSPHATE IONS CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION Iron, when immersed in a supply of aerated water which is slightly acid to slightly alkaline (pH 6.5-8.3), develops local anode and cathode sites on its surface. These sites or cells, formed as a result of impurities or intermolecular stresses in the iron, have a potential of 0.41 volt, which sponsors a current flow through the base metal and the electrolyte (water supply). At the anode iron is converted from metallic to ionic state, while at the cathode either ionic hydrogen or dissolved oxygen is reduced, causing the surface of the cathode to become alkaline, reference the following formulas:

(A) (Anode reaction) Fe Fe 2e (B) (Cathode Reactions) (1) Oxygen reduction 2e +H O+ /20 20H- (2) Ion reduction 2e 2H O 20H H (C) (Combining of the two electrode products yields ferrous hydroxide): Fe +2HO=Fe (H),,

1. Field of the Invention The process and composition are each adapted to the treatment of open and closed water systems such as may contain potable or non-potable flows. These objectives are adaptable to protection of ferrous and non-ferrous metals against corrosive waters, including variations between aerated soft meteorological and high total dissolved solids water supplies.

2. Description of the Prior Art The known prior art is best represented by U.S. Pat. No. 3,284,368 including a zinc and hexametaphosphate corrosion inhibitor. Calcium carbonate as an inhibitor is also currently practiced.

Other non-anticipatory art includes the following patents and publications:

2,080,299 Benning et 21 2,316,810 Romig 2,711,391 Kahler 2,793,932 Kahler 2,872,281 Kahler 2,900,222 Kahler 3,024,201 Bregman 3,116,178 Upham 3,120,425 Hatch 3,151,087 Ryznar et al 3,347,797 Kuegemann et al Butler; Ison; Corrosion and its Prevention in Waters,

Reinhold, 1966. Chap. 1, pp. 2

Uhlig; Corrosion and Corrosion Control, Wiley,

1965. Chap. 6, pp. 79

LaQue, Copson; Corrosion Resistance of Metals and Alloys, Reinhold, 2nd Ed., Chap. 4, pp. 83.

SUMMARY OF THE INVENTION A process and composition of matter effective in minimizing pitting and tuberculation on the interior surfaces of ferrous and non-ferrous water distribution plumbing systems. Corrosive waters ranging from aerated soft meteorological to high total dissolved solid supplies are initially treated herein through the introduction of small but effective quantities of zinc-sulfamate-orthophosphate" inhibitor whereby the inhibitor solution, when applied to the water, passivates the surface of the corroding interior metal of piping systems by depositing a zinc phosphate film thereover, effectively preventing difi'usion of dissolved oxygen. Selective diminution in application of the inhibitor solution to 1 ppm zinc, or less, in the corrosive water sustains the protective zinc phosphate film.

As either a potable or non-potable water addition, the zinc, sulfamic and phosphate ions would not exceed 3 ppm. The pH of the treated water is to be maintained at between 5 and 9; preferably for potable water at between 6.5 and 8.4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To explain the theory of passivation hereunder, consider the inhibitor at a dosage of 3 ppm zinc or less is being applied to a slightly acidic to slightly alkaline water (pH 6.5-8.3). Of the ions contained in the inhibitor, zinc, sodium, hydrogen, phosphate, sulfate and sulfamate, the zinc and phosphate ions tend to precipitate in the water environment but are usually in the colloidal state.

This compound is preferably so finely divided that it resists settling from the bulk of the electrolyte, and it can only be removed by centrifuging and ultrafltration. The zinc phosphate has a very important characteristic in that it adheres tenaciously to most of the common plumbing materials, i.e., metals, glass, plastic or rubber. Film studies on glass and metals have indicated a deposit in the order of a molecule thickness (1 X 10" in.) at zinc dosage rates of 1 ppm zinc added continuously to a flowing alkaline (pH 8.3) water supply. If the inhibitor is not applied at dosage values exceeding 2 to 3 ppm zinc, the film will not deposit on itself and accumulate as in the case of a thickly precipitated calcium carbonate scale.

Metals are protected by the present thinly deposited zinc phosphate film, which presumably is insoluble in water, and as such it restricts the corrosive effects of the gases, dissolved oxygen and carbon dioxide. This film attaches itself so firmly to materials that it cannot be easily washed or rubbed off. It is, of course, subject to the abrasive action of suspended solids in a flowing water stream and in the environment of a mineral or a strong fruit acid it dissolves. Thus, once a freshly installed metal is exposed to water treated with the inhibitor, it can be anticipated that the surface of the metal will be passivated and the process of normal metallic corrosion will be prevented. Existing pre-rusted or corroded metals will be afforded protection in such a treated water supply because of the passivation induced by the film deposited on the surfaces of the tubercules or other deposits. Once a plumbing system has become passivated, as is evidenced by the presence of the zinc phosphate at the extremities of the distribution system or termination of the metallic plumbing, the initial pre-coat dosage of inhibitor may be dropped to some low value so as to just maintain the deposited film and to protect against mechanical damage.

As indicated, the formulation develops the zinc, sulfamate and phosphate ions, through either a combination of zinc oxide, sulfamic acid and phosphoric acid or zinc sulfate, sulfamic acid and monosodium orthophosphate. Suitable sources for the zinc include zinc chloride, zinc oxide, zinc sulfate, metallic zinc, zinc carbonate, sodium zincate and/or zinc phosphate. Suitable sources for the phosphate ion includes orthophosphoric acid or salts of orthophosphoric acid. Sources of the sulfamate ion include principally sulfamic acid. This ion is important in part in retaining the zinc in solution against minor pH fluctuations.

The mol ratios are maintained, regardless of the starting product and are generally represented by the formula comprising 3 atoms of zinc to 2 mol s of phosphate, thus:

Assuming that the pH is maintained at between 5 and 9, a suitable liquid formulation containing approximately 3 atoms of zinc as zinc sulfate monohydrate (ZnSO. H O), one mol of anhydrous sulfamic acid (HNH SO and 3 mols of orthophosphoric acid (H PO diluted in water may be emloyed herein or a dry mixture may be prepared from zinc TABLE I.-EFFECI F pH 0N TURBIDITY OF COLORADO RIVER WATER AT VARIOUS TREATMENT LEVELS OF Sulfate y f with Sulfamic acid and sdium ZINC SULFATE-MONOSODIUM PHOSPHATE-S ULFAMIC phosphate, monobasic (Nail-1 1 0 ACID INHIBITOR One specific potable water formulation would include the Turbidity in Jackson turbidity units 1 following: zinc sulfate monohydrate 56 weight percent; Gold 0 Q) 2 Hot C.)

sulfamic acid at 20 weight percent and monosodium l p.p.m. 2 p.p.m. 3 p.p.m 1 p.p.m. 2 p.p.m. 3 p. .m. orthophosphate at 24 weight percent. Zinc Zinc zinc DH 3 mm zmc 1 00 2. 00 3.10 8. 4 1. 70 6. 2 7. 5 1. 40 1. 60 2. 70 8. 2 2. 70 7.1 7. 2 3ZnSO 2HNH2SO3 2N8H2PO4= 1.50 1.50 8.11) 5.40 $2 0.6 1. 0 l. 0 0 8. .40 .5 10.0 32 20 1. 50 1.50 a. :5 7. 0 15.30 0. 0 10.0 0. 0 1.10 3. 0 7.8 .40 0.0 23.0 2N3NH2SO3 BHZSO 0.88 1.05 2.70 7.7 2.50 7.5 17.0 386.10 238.18 294.12 0. 60 0. 76 2. 40 7. 6 l. 80 7. 2 16. 0 i a W V V W m 7 0.57 0.73 2. 50 7. 5 1. 50 7.3 18.0 W W 0. 38 0. 43 1. 80 7. 3 l. 70 4. 7 l7. 0 0.26 0 22 0.33 7.0 1.20 3.0 15.0 Ten gallons of an aqueous solution coma". g one Pound of 'Iurbidiity Jmelasure rlnerglsdimade filth 11 110011 Laboratory Turbidimeter are 11 ac son ur ty n s." per be prepared by addlng a 50 pound com I Turbidity rend cold (24 C.) and hot (80 C.). Tl1080 C. temperature posite of the ingredients to 8.25 gallons of water: was maintained for 3 hours before reading. W i 3 The pH adjustments worn made with 0.02N 111804 using 11 Fisher 'Iitralyzer. i V ZnSOAJ O 27.65 lbs. HNH,SO, 10.00 lbs. NaH PO. 12.35 lbs. TABLE II.EFFECT 0F SODIUM HEXAMEIAPHOSPHATE Total 50.00 ON TURBIDITY OF COLO RADO RIVER WATER AT VA RI- OUS TREATMENT LEVELS OF ZINC SULFATE-MONO 25 SODIUM PHOSPHATE SULFAMIC ACID INHIBITOR J i 1 The 1nh1b1tor solut1on has the followlng physical charac- Turbidity ackson turbidity 1m ts teristics: Cold (24 C.) 2 Hot (80 c 2 7 1 21?. 2 $530 3 $525 shirt? 1 3th fi'iic' 3 ""2125 Color water white Baum 5 73 iii 31% 1 5:5 2:3 7:? P 0174 1.5 2.15 2 2.2 5.3 7.0 0.68 1.5 2.8 3 1.8 5.2 7.3 0.53 1.4 2.7 4 1.8 4.7 7.2 Ten gallons of the above solution applied to one million gal- 35 8: g? 51g 2 i; 2% lons of water will supply zmc at a level of 1.2 parts per m1ll1on. 3.22 i: i f: g {g 2:? 2 0.42 0.59 1.7 0 1.6 2.7 5.3 As mentioned above, dosage of the inhibitor to a corrosive 0.37 0. 53 1. 7 10 2.0 2. 7 4.7 water should preferably be maintained initially at a zinc Turbidity measurements made with a Hach Laboratory Turbidicentration of 2 to 3 parts per million. This dosage should be 40 mgtqe r ago 1 1: lacg r giyg fig g g -z C T110800 C tem Mature maintained for a length of time as dictated by the level of 21116 was g p sampled at some remote point in the dlstribution system. 3 Sodium hexametaphosphate. When it has been determined that the zinc residual has ap- 4 m??? at Start f? i f' Proached the applied dosage, the treatment rate should be A specific example of the performance of the corrosion inreduced to a continuous zinc dosage of 1 part per million or hibi h i i f ll l SAE 1010 carbon steel coupons were exposed to 0.5 gallon per minute stream of water for 30 days. The corrosion rate of The liquid and dry inhibitor formulations for potable water h n- 1 specimen, untreated, was 35 7 dd illi are also satisfactory for non-potable water treatment. Some per square deimeter per da while the inhibitor treated add metaphosphaie addition might be necessary for specimen showed acorrosion rate of less than 1.0 mdd. inhibincnpotable Waters because of the Problems associated with tor film analysis showed that the treated specimen had been water concentrating (high tot l dis l e oli An xampl zinc phosphatized. The inhibitor formulation was added to the of this application would be for industrial, non-potable water w t r t am on a continuous basi resulting in a treatment re-circulating and single pass supply systems containing large level equivalent to 1 ppm zinc. quantities of salts, i.e., sea water. lclairn:

1. The composition of matter, useful as a corrosion inhibitor 11 has been found in l that the ofthophosphate is for ferrous and non-ferrous water conduits consisting essenmost desirable in contrast to the common metaphosphates and i ll f; i ulf ate and phosphate ions in mol ratio from polyphosphates- Th th p sp t iOn mp more about 3 mols zinc to 2 mols sulfamate to 2 mols phosphate, favorably for the me l in W r gh in chlorides andv wherein the zinc and phosphate ions precipitate in water havsulphates which normally tend to dissolve anode and cathode i a pH ofs 9 a zinc phosphate. rust deposits. Zinc orthophosphate per se, being insol l i8 2. The composition of matter of claim 1 wherein the zinc not affected by water temperature fluctuation and has the esions are derived from zinc chloride. sential effect of developing an oxygen impenetrable barrier at 3, The composition of matter of claim 1 in which the zinc the corrosion site. ions are derived from metallic zinc.

4. The composition of matter of claim 1 in which the zinc Tables 1 and ll demonstrate turbidity variations due to the ions are derived from zinc carbonate. efiect of pH and the presence of metaphosphate residual on 5. The composition of matter of claim 1 in which the zinc highly buffered water (Colorado River water) treated with ions are derived from sodium zincate. various dosages of inhibitor at l, 2 and 3 ppm zinc. Of particu- 6. The composition of matter of claim 1 in which the zinc is lar interest is the presence of metaphosphate which prevented derived from zinc sulfate monohydrate, the sulfamate is the interference of calcium carbonate precipitation due to the derived from sulfamic acid and the phosphate is derived from so-called threshold effect." The cold water temperature was monosodium orthophosphate. 24 C. while the hot water temperature of the samples was ad- 7. The composition of matter of claim 1 wherein the zinc justed to 80 C. for3hours. ions are derived from a zinc salt, the sulfamate ions are A. zinc sulfate monohydrate 50% B. sulfamic acid C. monosodium orthophosphate 24% 9. A composition aqueous solution useful as a corrosion inhibitor for ferrous and non-ferrous water conduits, the solution consisting essentially of in a water solution:

A. zinc sulfate monohydrate 56% B. sulfamic acid 20% C. orthophosphoric acid,

strength 24% UNITED STATES PATENT armor CETFECAE CO EC'MQN Patent No. 3,669,901 D8133 June ll. 1972 Inventor(s) William Bruce Murray It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover page, in the paragraph immediately following the title "Related U.S. Application Data" the word "abandoned" incorrectly appears after the words "Ser. No. 76,221, Sept. 8, 1970," and should be deleted, so that the paragraph should read:

" [60] Division of Ser. No. 76,221, Sep'g. 8 l 9j,

May 5, 1969, abandoned."

Signed and sealed this 27th day of February 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK v Attesting Officer Commissioner of Patents Continuation-in-part of Ser'. No. 829,842,

UNITED STATES PATENT QFFICE CERTIFICATE OF COEC'HN' Patent No. 3,669,901 Dated June 11. 1972 Inventor(s) William Bruce Murray It is certified that error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover page, in the paragraph immediately following'the title "Related U.S. Application Data" the word "abandoned" incorrectly appears after the words "Ser. No. 76,221, Sept. 8, 1970," and should be deleted, so that the paragraph should read:

" [60] Division of Ser. No. 76,221, sepg. g l 9jg,

May 5, 1969, abandoned."

Signed and sealed this 27th day of February 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCI-LALK Attesting Officer Commissioner of Patents Continuation-in-part of Ser. No. 829 "Wm 7 

2. The composition of matter of claim 1 wherein the zinc ions are derived from zinc chloride.
 3. The composition of matter of claim 1 in which the zinc ions are derived from metallic zinc.
 4. The composition of matter of claim 1 in which the zinc ions are derived from zinc carbonate.
 5. The composition of matter of claim 1 in which the zinc ions are derived from sodium zincate.
 6. The composition of matter of claim 1 in which the zinc is derived from zinc sulfate monohydrate, the sulfamate is derived from sulfamic acid and the phosphate is derived from monosodium orthophosphate.
 7. The composition of matter of claim 1 wherein the zinc ions are derived from a zinc salt, the sulfamate ions are derived from sulfamic acid and the phosphate ions are derived from sodium phosphate.
 8. A composition of matter, useful as a corrosion inhibitor for ferrous and non-ferrous water conduits, comprising: A. zinc sulfate monohydrate 50% B. sulfamic acid 20% C. monosodium orthophosphate 24%
 9. A composition aqueous solution useful as a corrosion inhibitor for ferrous and non-ferrous water conduits, the solution consisting essentially of in a water solution: A. zinc sulfate monohydrate 56% B. sulfamic acid 20% C. orthophosphoric acid, 85% strength 24% 